The present invention relates to a rubber composition for breaker, in particular, a rubber composition for breaker having well-balanced properties among rigidity, heat resistance, adhesiveness, humid aging adhesion and elongation property, and a pneumatic tire having a breaker layer or a belt layer comprising the rubber composition.
In recent years, there is a growing demand for life extension of tires, and it has been tried to improve abrasion resistance of cap tread rubber or to enlarge tread width of a tire. However, this increases heat build-up characteristics of a tire, causing hardening of the breaker rubber or decrease of elongation at break, which results in problems such as burst phenomenon of tire or that separation between a tread and a belt is easily caused.
For improving these situations, it is effective to bring down the heat build-up characteristics of the cap tread, but it then becomes difficult to meet the demand for the abrasion resistance. In addition, there is another general technique of forming a two-layered tread of a cap and a base using a low heat build-up compound for the base tread. However, low heat build-up rubbers usually have poor reinforcing capability, and therefore abrasion resistance decreases when the base tread is exposed at a late stage of abrasion, causing poor abrasion appearance (chipping) or crack at the bottom of the groove. Therefore, the low heat build-up rubber can be used only in such an amount that it is not exposed to the surface in case of wearing, and lowering effect on heat build-up remains small.
Accordingly, there are urgent needs for a rubber compound for breaker durable to such high heat build-up conditions for a tread rubber.